A near-consensus among private economists is that Japanese inflation measured by the core CPI—the BOJ’s preferred gauge—will slow from here as a boost from the yen’s past weakness has run its course. That would leave the central bank no choice but to print even more money to meet its target of 2% inflation, some economists say.

But Mr. Kuroda suggested that was not the case in a speech Monday to a leading Japanese business lobby, Keizai Doyukai.

The core index is “expected to slow to around 1%” through the summer before accelerating again, Mr. Kuroda said. In this context he reiterated his mantra that the core inflation will stay “around 1.25%” for some time.

“By making it clear that ’1%’ would be within the definition of ‘around 1.25%,’ Mr. Kuroda signaled that he won’t do anything” even if the index moves closer to the 1% mark, said Yoshimasa Maruyama, a senior policy analyst at Itochu Corp.

Mr. Kuroda’s remarks may be a pre-emptive step to keep speculation for additional easing measures in check, in case coming price data signal moderating inflation pressure. A central bank generally dislikes strong speculation over its policy action, as it can complicate policy-making by destabilizing markets and sometimes force it to act even against its will.

Core CPI data due for release Friday will likely show a 1.4% increase in May, adjusted for a sales tax increase that took effect the previous month, according to economists polled by The Wall Street Journal and the Nikkei. That would mark the first slowdown in eight months. In April, the index climbed an adjusted 1.5%–the biggest rise in five and a half years–as firms took advantage of the tax increase and solid domestic demand and passed on long-delayed price markups to consumers, economists say.

Mr. Kuroda explained his confidence using a variant of the Phillips Curve that mapped the relationship between inflation and the output gap, a measure of slack in an economy.

In a normal economy, the curve is sloped upward, and prices increase when there is no economic slack. In Japan, the curve has been sloped upward, but as a result of entrenched deflation, the entire curve has shifted sharply downward over years, which has made it hard for prices to rise even when there is no output gap, Mr. Kuroda said. Yet, signs are emerging that the curve “has started to drift upward” in Japan, he said, attributing the transformation to rising inflation expectations among the Japanese.

But even if Mr. Kuroda sounds confident, stronger speculation for fresh easing will emerge if the adjusted core CPI falls below 1%. In an interview with The Wall Street Journal last month, Mr. Kuroda indeed declared that the core CPI wouldn’t fall below 1%. And some BOJ officials think a break below 1% would require a policy response, according to people familiar with the bank’s thinking.

The BOJ’s price goal may be 2%, but the 1% level is increasingly seen as a de facto threshold for action.

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